(CBS) It's a medical mystery that has baffled scientists for nearly two decades. How do some HIV-infected people, about one in 300, keep the virus at such a low level that they don't get sick with full blown AIDS, even if they don't take medicine?
Now, researchers at Massachusetts General Hospital and Harvard University think they have a clue.
It's in the genes, they say, specifically five amino acids in a protein called HLA-B.
"We found that, of the three billion nucleotides in the human genome, just a handful make the difference between those who can stay healthy in spite of HIV infection and those who, without treatment, will develop AIDS," said study co-author Dr. Bruce Walker, MD, director of the Ragon Institute, in a statement.
Never heard of HLA-B?
Well, the protein plays a vital role in the immune system by grabbing onto pieces of a virus and bringing them into the cell membrane where they get tagged for destruction by "killer" T cells. Researchers believe the shape and structure of five critical amino acids on HLA-B help determine whether the immune system can outfox HIV viruses or not.
At this point it's high science, but understanding how some people naturally fight HIV, researchers say, is critical to curing it for everyone else.
"We have a long way to go before translating this into a treatment for infected patients and a vaccine to prevent infection," Walker said, "but we are an important step closer."
The study was published in Science.
Anyone infected with HIV, who has a low viral load without medicine is encouraged to join the study. Find out here.